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Lives of the Other Mollusks 49
frequently eaten by peoples of the Mediterranean area and the Orient but to
a much lesser extent by Americans.
In contrast to the speedy squid, the octopus is relatively a slow-moving
creature, although it can swim away at a fairly rapid rate by using the same
water-jet system of propulsion; it lacks the caudal fins of the squid. The
underside of the eight arms of the octopus are studded along their entire
lengths with cup-like disks or acetabula. When a sucker is pressed against
any smooth surface, the center is withdrawn to create a vacuum which en-
sures a powerful attachment. An octopus can "tentacle" along with remark-
able agility and at night may even take to short excursions out of water. I
have known of an octopus kept in a small aquarium in Bermuda to push the
lid off the top, crawl down the table and off the veranda in an attempt to
reach the ocean. It crawled more than a hundred feet toward the sea before
it succumbed and was attacked by ants. There have been many authentic
accounts of encounters with octopus on exposed tidal reefs, and a few ob-
servers state that the octopus can keep up with a man in a brisk walk.
Even more astounding than the locomotive powers of the cephalopods
are their amazing displays of bright, glowing lights and color changes. The
shallow-water species have embedded in their skin chromatophores whose
expansion and contraction are controlled by the nervous system. Emotion,
excitation or response to the color of surrounding objects will effect the
color changes in the octopus. Among the deep-water squid, many of which
are phosphorescent, gorgeous underwater pyrotechnics are frequently dis-
played which far outshine the brightest of fireflies and glowworms. Specimens
of Lycoteuthis brought up from considerable depths and kept alive in chilled
water have had their photographs taken by their own light. The body looks
as if it were adorned by a diadem of brilliant gems. The middle organs of
the eyes shine with ultramarine blue, the lateral ones with a pearly sheen.
Those toward the front of the lower surface of the body give out a ruby-red
light, while those behind are snow-white or pearly, with the exception of
the middle organ which is sky-blue. Some squid have astonishingly com-
plex bull's-eye lanterns; others have mirrored searchlights. A species of Heter-
oteuthis is able to spurt out a luminous secretion from its funnel and the
jet of water following it draws out the bright globules into long, shining
threads.
The sexes in the cephalopods are separate, except for two or three
isolated examples. In most of the species females are much more numerous,
the ratio of females to males being loo to 15 in some species of the Loligo
squid and 100 to 25 in some of the Octopus. The most outstanding feature
is the morphological differences between the two sexes. In the Argonauta
or Paper Nautilus, the females are 10 to 15 times as large as the males which
completely lack the beautiful shell used by females for storing eggs. The